SCP-XXXX, although somewhat dangerous, can be easily contained within a small personnel locker, but is restricted to personnel of Clearance Level 2 or above due to potential misuse.

This is not clinical tone at all. I'd try: "SCP-XXXX is to be contained within a small low security containment locker at Site-XX. Access to SCP-XXXX is restricted to personnel with level 2 clearance or higher."

This way, the reader of the document not only knows how the item is contained, where it is contained, but who can access it. All the stuff you'd need in a technical document.

SCP-XXXX appears at first to be a bottle of "██████ Sparkling Water" and displays no anomalous properties. However, upon close inspection, the ingredients on the product's label seem to change at random intervals; see Addendum XXXX-3 for list of 'ingredients' observed during testing.

Again, we are breaking clinical tone here. Keep in mind that the Foundation is a first and foremost a research institution. They are not going to say something at first appears to be X, they are going to say something is or is not something. I'd try:

"SCP-XXXX is a bottle of [BlackBox] brand sparkling water. SCP-XXXX's anomalous properties become apparent upon reading the bottle's ingredient label, which changes content at random intervals ranging between XX and XX [unit of time]. An extensive list of noted ingredients can be found in Addenda 3."

Additionally, its not wise to black box something unless you have a reason to do so. Just include the name of the brand.

It's primary anomalous effect however is its ability to make anyone reading the ingredients list believe themselves allergic to any ingredient read, regardless of the fact that no physical change has taken place. It also manifests in the form of a compulsion to continue reading the ingredients despite knowledge that doing so will make them allergic.

Yet again we have a lack of clinical tone in our clinical document I'd maybe try:

"Upon reading of the ingredient's list, subject's experience a memetic effect in which they believe themselves allergic to the ingredients listed therein. Despite this belief, no evidence has been discovered that the subject's immune system will respond with an allergic reaction to the associated stimuli."

Now that we have gotten through the description. Onto the addenda.

D-Class reads out glass, nitrogen, and [DATA EXPUNGED], before stating that he'll keep reading. Before he can do so, he appears to be attempting to sneeze repeatedly, and seems to be crying. When asked what what is happening, he replies, through various attempted sneezes, that he's allergic to nitrogen and that there's nitrogen in the room. D-████-3227 removed from testing area and placed in argon-oxygen environment. Sneezing and eye-watering immediately ceases.

I have multiple problems with this. First off, why would glass be listed as an ingredient? What type of glass? Secondly, why are you including that Data Expunged? Id doesn't seem to serve any purpose, just show the info. Finally, considering how much of the earth's atmosphere is made of nitrogen, there are going to be much more dire effects for someone becoming allergic. What would those be? You set up this horrible event, now follow through.

Addendum two, in my opinion, doesn't really add much, and can probably be included in addendum one. Addendum three has potential, however, the descriptions of the reactions are a little convoluted as is, and could afford to be summarized in one or two sentences tops.

Overall, this draft didn't do much for me. Its just a generic memetic effect paired with a compulsive effect. Combined with a slew of grammar and formatting mistakes, and blackboxing for the sake of blackboxing, I think this could do with a rewrite.

Made some changes based on your response. More clinical, and I merged addendum 2 with 1. I also scrapped what I had under the expungement and replaced it with salt, which will probably get changed again in the future. Also, I was under the impression that brands, dates, names, etc were blackboxed; is this incorrect?